Showing papers on "Infrared dark cloud published in 2015"
TL;DR: In this article, the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, were investigated using the ALMA.
Abstract: Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3mm continuum and spectral line emission using the ALMA. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 10^3 AU. Spectral line emission from C18O, CH3OH, 13CS, H2CO and N2D+ are detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH3OH, H2CO and SO emissions. The parsec-scale kinematics in NH3 exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the 1\sigma dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.
184 citations
TL;DR: In this article, the authors present evidence for additional bones in the Milky Way, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure.
Abstract: Recently, Goodman et al. argued that the very long, very thin infrared dark cloud "Nessie" lies directly in the Galactic midplane and runs along the Scutum–Centaurus Arm in position–position–velocity (p–p–v) space as traced by lower-density and higher-density gas. Nessie was presented as the first "bone" of the Milky Way, an extraordinarily long, thin, high-contrast filament that can be used to map our Galaxy's "skeleton." Here we present evidence for additional bones in the Milky Way, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure. Our 10 bone candidates are all long, filamentary, mid-infrared extinction features that lie parallel to, and no more than 20 pc from, the physical Galactic mid-plane. We use , and radial velocity data to establish the three-dimensional location of the candidates in p–p–v space. Of the 10 candidates, 6 also have a projected aspect ratio of ≥50:1; run along, or extremely close to, the Scutum–Centaurus Arm in p–p–v space; and exhibit no abrupt shifts in velocity. The evidence presented here suggests that these candidates mark the locations of significant spiral features, with the bone called filament 5 ("BC_18.88-0.09") being a close analog to Nessie in the northern sky. As molecular spectral-line and extinction maps cover more of the sky at increasing resolution and sensitivity, it should be possible to find more bones in future studies.
84 citations
TL;DR: In this paper, the fragmentation and gravitational collapse of dense cores in infrared dark clouds (IRDCs) were studied using submillimeter continuum and spectral line data as well as multiple inversion transitions of NH3 and H2O maser data of four massive clumps in G28.53.
Abstract: To study the fragmentation and gravitational collapse of dense cores in infrared dark clouds (IRDCs), we have obtained submillimeter continuum and spectral line data as well as multiple inversion transitions of NH3 and H2O maser data of four massive clumps in IRDC G28.53−0.25. Combining single-dish and interferometer NH3 data, we derive a rotation temperature of G28.53. We identity 12 dense cores at a 0.1 pc scale based on submillimeter continuum, and obtain their physical properties using NH3 and continuum data. By comparing the Jeans masses of cores with the core masses, we find that turbulent pressure is important for supporting the gas when 1 pc scale clumps fragment into 0.1 pc scale cores. All cores have a virial parameter that is smaller than 1 if we assume an inverse squared radial density profile, suggesting they are gravitationally bound, and the three most promising star-forming cores have a virial parameter that is smaller than 1 even when taking the magnetic field into account. We also associate the cores with star formation activities revealed by outflows, masers, or infrared sources. Unlike what previous studies have suggested, MM1 turns out to harbor a few star-forming cores and is likely a progenitor of a high-mass star cluster. MM5 is intermediate while MM7/8 are quiescent in terms of star formation, but they also harbor gravitationally bound dense cores and have the potential for forming stars, as in MM1.
37 citations
TL;DR: In this article, a region in the N2H + (1-0) line was mapped to trace the core kinematics with an angular resolution of 2 00 and velocity resolution of 0.110.
Abstract: We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC) G011.110.12 containing young, star-forming cores. In addition to the 3.2 mm continuum emission from cold dust, we map this region in the N2H + (1-0) line to trace the core kinematics with an angular resolution of 2 00 and velocity resolution of 0.2 km s 1 . These data are presented in concert with recent Herschel results, single-dish N2H + (1-0) data, SABOCA 350 m continuum data, and maps of the C 18 O (2-1) transition obtained with the IRAM 30 m telescope. We recover the star-forming cores at 3.2 mm continuum, while in N2H + they appear at the peaks of extended structures. The mean projected spacing between N2H + emission peaks is 0.18 pc, consistent with simple isothermal Jeans fragmentation. The 0.1 pc-sized cores have low virial parameters on the criticality borderline, while on the scale of the whole region, we infer that it is undergoing large-scale collapse. The N2H + linewidth increases with evolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of all tracers are in excellent agreement, except in the starless region where two N2H + velocity components are detected, one of which has no counterpart in C 18 O. We suggest that gas along this line of sight may be falling into the quiescent core, giving rise to the second velocity component, possibly connected to the global collapse of the region.
33 citations
TL;DR: In this article, the spectral energy distribution of SDC335-MM1 and MM2 was analyzed with the Australia Telescope Compact Array (ATCA) and the authors found that the measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the ZAMS spectral type assigned to them, suggesting that a mechanism is limiting the accretion luminosity.
Abstract: Aims. Recent ALMA observations identified one of the most massive star-forming cores yet observed in the Milky Way: SDC335-MM1, within the infrared dark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in the early stages of its star formation process. We aim to constrain the properties of the stars forming within these two massive millimetre sources.
Methods. Observations of SDC335 at 6, 8, 23 and 25 GHz were made with the Australia Telescope Compact Array. We report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (SEDs) of the compact sources in SDC335.
Results. Three hyper-compact Hii regions within SDC335 are identified, two of which are within the MM1 core. For each HCHii region, we fit a free-free emission curve to the data, providing the derivation of the sources’ emission measure, ionising photon flux, and electron density. Using these physical properties we assign each HCHii region a zero-age main sequence (ZAMS) spectral type, finding two protostars with characteristics of spectral type B1.5 and one with a lower limit of B1–B1.5. Ancillary data from infrared to mm wavelength are used to construct free-free component subtracted SEDs for the mm-cores, which allows us to calculate the bolometric luminosities and revise the previous gas mass estimates.
Conclusions. The measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the ZAMS spectral type assigned to them. The protostars are still actively accreting, suggesting that a mechanism is limiting the accretion luminosity. We present the case for two different mechanisms capable of causing lower than expected accretion luminosity. Finally, using the ZAMS mass values as lower limit constraints, a final stellar population for SDC335 was synthesised finding SDC335 is likely to be in the process of forming a stellar cluster comparable to the Trapezium cluster and NGC 6334 I(N).
19 citations
TL;DR: In this article, a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region was presented, where the authors used a combination of ground-based near-infrared, space-based infrared and X-ray data to construct a point source catalog from which they identified 226 young stellar sources.
Abstract: We present a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region. We studied young stars forming or recently formed at and around the tip of a prominent molecular pillar and an infrared dark cloud. Using a combination of ground based near-infrared, space based infrared and X-ray data, we constructed a point source catalog from which we identified 226 young stellar sources, which we classified into evolutionary classes. We studied their spatial distribution across the molecular gas structures and identified several groups possibly belonging to distinct young star clusters. We obtained samples of these groups and constructed K-band luminosity functions that we compared with those of artificial clusters, allowing us to make first order estimates of the mean ages and age spreads of the groups. We used a $^{13}$CO(1-0) map to investigate the gas kinematics at the prominent gaseous envelope of the central cluster in DR15, and we infer that the removal of this envelope is relatively slow compared to other cluster regions, in which gas dispersal timescale could be similar or shorter than the circumstellar disk dissipation timescale. The presence of other groups with slightly older ages, associated with much less prominent gaseous structures may imply that the evolution of young clusters in this part of the complex proceeds in periods that last 3 to 5 Myr, perhaps after a slow dissipation of their dense molecular cloud birthplaces.
16 citations
TL;DR: In this article, the authors present a point-source catalog of IRDC G53.2 that contains ∼370 sources from their photometry of the Spitzer MIPS 24 μm data and the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Catalog.
Abstract: We present star formation activity in the infrared dark cloud (IRDC) G53.2, a remarkable IRDC located at Galactic coordinates based on the census of young stellar object (YSO) candidates. IRDC G53.2 was previously identified as several IRDCs in mid-IR images, but it is in fact a long ( pc) cloud, well consistent with a CO cloud at km s−1 (or at kpc). We present a point-source catalog of IRDC G53.2 that contains ∼370 sources from our photometry of the Spitzer MIPS 24 μm data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Catalog. The classification of the identified sources based on their spectral index and control field analysis to remove field star contamination reveals that IRDC G53.2 is an active star-forming region with ∼300 YSO candidates. We compare the YSO classification based on spectral index, mid-IR colors, and the wavelength range used, which results in consistent classification, except for flat-spectrum objects, with some ambiguity between Class I and II. Comparison of the YSO population in IRDC G53.2 with those of other nearby star-forming clusters indicates that they are similar in age; on the other hand, stronger association with mid-IR stellar sources in IRDC G53.2 compared with other IRDCs indicates that IRDC G53.2 is at a later evolutionary stage among IRDCs. Spatial distribution of the YSO candidates in IRDC G53.2 shows a good correlation with 13CO column density and far-IR emission, and earlier-class objects tend to be more clustered in the regions with higher density.
14 citations
TL;DR: In this article, a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region was presented, where the authors used a combination of ground-based near-infrared, space-based infrared and X-ray data to construct a point source catalog from which they identified 226 young stellar sources.
Abstract: We present a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region. We studied young stars forming or recently formed at and around the tip of a prominent molecular pillar and an infrared dark cloud. Using a combination of ground based near-infrared, space based infrared and X-ray data, we constructed a point source catalog from which we identified 226 young stellar sources, which we classified into evolutionary classes. We studied their spatial distribution across the molecular gas structures and identified several groups possibly belonging to distinct young star clusters. We obtained samples of these groups and constructed K-band luminosity functions that we compared with those of artificial clusters, allowing us to make first order estimates of the mean ages and age spreads of the groups. We used a $^{13}$CO(1-0) map to investigate the gas kinematics at the prominent gaseous envelope of the central cluster in DR15, and we infer that the removal of this envelope is relatively slow compared to other cluster regions, in which gas dispersal timescale could be similar or shorter than the circumstellar disk dissipation timescale. The presence of other groups with slightly older ages, associated with much less prominent gaseous structures may imply that the evolution of young clusters in this part of the complex proceeds in periods that last 3 to 5 Myr, perhaps after a slow dissipation of their dense molecular cloud birthplaces.
9 citations
TL;DR: In this paper, a point-source catalog of IRDC G53.2 is presented based on the census of young stellar object (YSO) candidates, and the classification of the identified sources based on their spectral index and control field analysis to remove field star contamination is performed.
Abstract: We present star formation activity in the infrared dark cloud (IRDC) G53.2, a remarkable IRDC located at Galactic coordinates $(l,b)\sim(53^{\circ}.2,\,0^{\circ}.0)$ based on the census of young stellar object (YSO) candidates. IRDC G53.2 was previously identified as several IRDCs in mid-IR images, but it is in fact a long ($\gtrsim$45 pc) cloud, well consistent with a CO cloud at $v\sim23$ \kms\ (or at $d\sim$1.7 kpc). We present a point-source catalog of IRDC G53.2 that contains $\sim$370 sources from our photometry of the {\it Spitzer} MIPS 24 \um\ data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Catalog. The classification of the identified sources based on their spectral index and control field analysis to remove field star contamination reveals that IRDC G53.2 is an active star-forming region with $\sim$300 YSO candidates. We compare the YSO classification based on spectral index, mid-IR colors, and the wavelength range used, which results in consistent classification, except for flat-spectrum objects, with some ambiguity between Class I and II. Comparison of the YSO population in IRDC G53.2 with those of other nearby star-forming clusters indicates that they are similar in age; on the other hand, stronger association with mid-IR stellar sources in IRDC G53.2 compared with other IRDCs indicates that IRDC G53.2 is at a later evolutionary stage among IRDCs. Spatial distribution of the YSO candidates in IRDC G53.2 shows a good correlation with $^{13}$CO column density and far-IR emission, and earlier-class objects tend to be more clustered in the regions with higher density.
7 citations
TL;DR: In this paper, spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation are presented.
Abstract: We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3–8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14–38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffuse Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR–FIR opacity laws that lack the ~12 and ~35 μm features associated with the thick water ice mantle models of Ossenkopf & Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.
6 citations
TL;DR: In this paper, the fragmentation and gravitational collapse of dense cores in infrared dark clouds (IRDCs) were studied using submillimeter continuum and spectral line data as well as multiple inversion transitions of NH3 and H2O maser data of four massive clumps.
Abstract: To study the fragmentation and gravitational collapse of dense cores in infrared dark clouds (IRDCs), we have obtained submillimeter continuum and spectral line data as well as multiple inversion transitions of NH3 and H2O maser data of four massive clumps in an IRDC G28.53-0.25. Combining single dish and interferometer NH3 data, we derive the rotation temperature of G28.53. We identity 12 dense cores at 0.1 pc scale based on submillimeter continuum, and obtain their physical properties using NH3 and continuum data. By comparing the Jeans masses of cores with the core masses, we find that turbulent pressure is important in supporting the gas when 1 pc scale clumps fragment into 0.1 pc scale cores. All cores have a virial parameter smaller than 1 assuming a inverse squared radial density profile, suggesting they are gravitationally bound, and the three most promising star forming cores have a virial parameter smaller than 1 even taking magnetic field into account. We also associate the cores with star formation activities revealed by outflows, masers, or infrared sources. Unlike what previous studies suggested, MM1 turns out to harbor a few star forming cores and is likely a progenitor of high-mass star cluster. MM5 is intermediate while MM7/8 are quiescent in terms of star formation, but they also harbor gravitationally bound dense cores and have the potential of forming stars as in MM1.
TL;DR: In this article, the spectral energy distributions of SDC335-MM1 and MM2 were derived from the ATCA data at 6, 8, 23 and 25 GHz.
Abstract: Recent ALMA observations identified one of the most massive star-forming cores yet observed in the Milky Way; SDC335-MM1, within the infrared dark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in the early stages of its star formation process. In this paper we aim to constrain the properties of the stars forming within these two massive millimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with the ATCA. We report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (SEDs) of the compact sources in SDC335. Three HCHII regions within SDC335 are identified, two within the MM1 core. For each HCHII region, a free-free emission curve is fit to the data allowing the derivation of the sources' emission measure, ionising photon flux and electron density. Using these physical properties we assign each HCHII region a ZAMS spectral type, finding two protostars with characteristics of spectral type B1.5 and one with a lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are used to construct free-free component subtracted SEDs for the mm-cores, allowing calculation of the bolometric luminosities and revision of the previous gas mass estimates. The measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the ZAMS spectral type assigned to them. The protostars are still actively accreting, suggesting that a mechanism is limiting the accretion luminosity, we present the case for two different mechanisms capable of causing this. Finally, using the ZAMS mass values as lower limit constraints, a final stellar population for SDC335 was synthesised finding SDC335 is likely to be in the process of forming a stellar cluster comparable to the Trapezium Cluster and NGC6334 I(N).
01 Aug 2015
TL;DR: In this article, the authors presented the 12CO J=1−0, 13CO J = 1−0 and C18O J= 1 −0 maps of the M17 giant molecular clouds (GMCs) obtained as a part of the Nobeyama 45m CO Galactic Plane Survey.
Abstract: We present the 12CO J=1–0, 13CO J=1–0, and C18O J=1–0 maps of the M17 giant molecular clouds (GMCs) obtained as a part of the Nobeyama 45m CO Galactic Plane Survey. The observations cover the entire area of M17 SW and M17 N clouds at an angular resolution of ~ 15″ which corresponds to ~ 0.15 pc. We found that the N cloud consists of a couple of twisted filaments, they are extended in parallel toward the Hii region. The typicall width of the filaments is ~0.5 pc in 13CO intensity map. Most of young stellar objects (YSOs) are located on the filaments which have a bright rim structure in 8μm at the filament edge facing the Hii region. Furthermore, the time scale of the YSOs formation on the bright rim is comparable with that of NGC 6618 cluster which provides UV photons for the region. This fact indicates that the cluster triggered to form YSOs in N cloud. We also investigated the geometry of the Hii region and GMCs by comparing spatial distribution of 12CO velocity channel map and infrared dark cloud, and then found that NGC 6618 is possibly formed by the cloud cloud colision.
TL;DR: In this paper, deep radio continuum observations of the star-forming core of the Serpens South Infrared Dark Cloud with the Karl G. Jansky Very Large Array (VLA) were conducted in two bands centered at 7.25 GHz and 4.75 GHz with an rms of 8.5 and 11.1 microJy/beam, respectively.
Abstract: We present deep radio continuum observations of the star-forming core of the Serpens South Infrared Dark Cloud with the Karl G. Jansky Very Large Array (VLA). Observations were conducted in two bands centered at 7.25 GHz (4.14 cm) and 4.75 GHz (6.31 cm) with an rms of 8.5 and 11.1 microJy/beam, respectively. We also use 2MASS, Spitzer and Herschel data to put our radio observations in the context of young stellar populations characterized by near and far infrared observations. Within a 5 arcmin x 5 arcmin region of interest around the central cluster, we detect roughly eighteen radio sources, seven of which we determine are protostellar in nature due to their radio spectral indices and their association with infrared sources. We find evidence for a previously undetected embedded Class 0 protostar and reaffirm Class 0 protostellar classifications determined by previous millimeter wavelength continuum studies. We use our infrared data to derive mid-infrared luminosities for three of our protostellar sources and find relative agreement between the known YSO radio luminosity vs bolometric luminosity correlation. Lastly, we marginally detect an additional six radio sources at the 2-3 sigma level that lie within two arcseconds of infrared YSO candidates, providing motivation for higher sensitivity studies to clarify the nature of these sources and further probe embedded and/or low luminosity YSOs in Serpens South.